1. Field of the Invention
The present invention relates to a multi-hop relay Broadband Wireless Access (BWA) communication system. More particularly, the present invention relates to a method of configuring a Relay-Frame Control Header (R-FCH).
2. Description of the Related Art
In the next generation communication system, known as the 4th Generation (4G) communication system, research is actively in progress to provide a Quality of Service (QoS) with a data transfer speed of about 100 Mbps. In particular, in a Broadband Wireless Access (BWA) communication system, such as a wireless Local Area Network (LAN) system and a wireless Metropolitan Area Network (MAN) system, research is being conducted on a communication system that supports a high speed service while ensuring mobility and QoS. Examples of such a communication system are an Institute of Electrical and Electronics Engineers (IEEE) 802.16d communication system and an IEEE 802.16e communication system, each of which standard is hereby incorporated by reference.
The IEEE 802.16d communication system, as well as the IEEE 802.16e communication system, employs an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme so that a physical channel of the wireless MAN system can support a broadband access network. The IEEE 802.16d communication system is implemented in consideration of only a single cell structure in a state that a Subscriber Station (SS) is fixedly located. That is, a mobility of the SS is not taken into consideration. Unlike the IEEE 802.16d communication system, the IEEE 802.16e communication system considers the mobility of the SS. A mobile SS will hereinafter be referred to as a Mobile Station (MS).
FIG. 1 is a schematic view illustrating a configuration of a conventional IEEE 802.16e communication system.
Referring to FIG. 1, the IEEE 802.16e communication system, which has a multi-cell structure, includes cells 100 and 150, Base Stations (BSs) 110 and 140 for respectively managing the cells 100 and 150, and a plurality of MSs 111, 113, 130, 151, and 153. Signal communication between the BSs 110 and 140 and the MSs 111, 113, 130, 151, and 153 is performed by using the OFDM/OFDMA scheme. Among the MSs 111, 113, 130, 151, and 153, the MS 130 is located in a boundary area (i.e., handover area) between the cell 100 and the cell 150. Thus, when the MS 130 moves towards the cell 150 managed by the BS 140 while performing signal communication with the BS 110, the BS that serves the MS 130 changes from the BS 110 to the BS 140.
Since signaling is performed between an MS and a fixed BS via a direct link as shown in FIG. 1, a highly reliable wireless communication link can be established between the BS and the MS in the conventional IEEE 802.16e communication system. However, due to the fixed location of the BS in the IEEE 802.16e communication system, a wireless network cannot be configured with high flexibility. Thus, there is a limitation in that communication services cannot be effectively provided in a wireless environment where traffic distribution and call demands rapidly change.
These problems may be addressed by applying a multi-hop relay data transmission scheme to a conventional cellular wireless communication system such as the IEEE 802.16e communication system by using fixed Relay Stations (RSs), mobile RSs, or general MSs. In a multi-hop relay wireless communication system, a network can be rapidly reconfigured in response to a change in the surrounding environment and the entire wireless network can be further effectively managed. For example, the multi-hop relay wireless communication system can expand cell coverage and increase system capacity. That is, when a channel state is poor between a BS and an MS, an RS may be installed between the BS and the MS so that a multi-hop relay path is formed through the RS, thereby providing the MS with a wireless channel having a better channel state. Moreover, since the multi-hop relay scheme may be used in a cell boundary area, where a channel state between a BS and an MS is poor, it is possible to provide a high-speed data channel and to expand cell coverage.
A configuration of a conventional multi-hop relay wireless communication system for expanding a BS coverage area will now be described.
FIG. 2 is a schematic view illustrating a configuration of a conventional multi-hop relay BWA communication system for expanding a BS coverage area.
Referring to FIG. 2, the multi-hop relay BWA communication system, which is configured in a multi-cell structure, includes cells 200 and 240, BSs 210 and 250 for respectively managing the cells 200 and 240, a plurality of MSs 211 and 213 located inside a coverage area of the cell 200, a plurality of MSs 221 and 223 managed by the BS 210 but located in an area 230 outside the cell 200, an RS 220 for providing a multi-hop relay path between the BS 120 and the MSs 221 and 223 located inside the area 230, a plurality of MSs 251, 253, and 255 located inside a coverage area of the cell 240, a plurality of MSs 261 and 263 managed by the BS 250 but located in an area 270 outside the cell 240, and an RS 260 for providing a multi-hop relay path between the BS 250 and the MSs 261 and 263 located inside the area 270, The OFDM/OFDMA scheme is used when signal communication is performed among the BSs 210 and 250, the RSs 220 and 260, and the MSs 211, 213, 221, 223, 251, 253, 255, 261, and 263.
In the multi-hop relay BWA communication system of FIG. 2, the RSs 220 and 260 may be infrastructure RSs, which are installed by service providers and thus known and managed by the BSs 210 and 250. Alternatively, the RSs 220 and 260 may be client RSs which act as user terminals (i.e., SSs or MSs) or may be RSs according to other circumstances. Furthermore, the RSs 220 and 260 may be fixed RSs, or nomadic RSs (e.g., laptop computers) having nomadic capability, or mobile RSs having the same mobility as MSs.
When an RS is used to expand a cell area, a frame structure among a BS, the RS and an MS has to be defined by expanding a conventional frame structure defined between the BS and the MS. That is, the BS has to define a frame structure such that communication between RSs and MSs can be achieved based on one communication platform. For this, a Downlink (DL) frame of the BS is divided into a BS-MS area, in which communication is performed between a BS and an MS, and a BS-RS area in which communication is performed between a BS and an RS. Likewise, an Uplink (UL) frame of the BS is divided into an MS-BS area, in which communication is performed between an MS and a BS, and an RS-BS area in which communication is performed between an RS and a BS. The BS transmits to the MS a MAP including allocation information on the BS-MS area. Further, the BS transmits to the MS a Frame Control Header (FCH) including information required to decode the MAP. The FCH transmitted to the MS by the BS will hereinafter be simply referred to as M-FCH. The M-FCH has a format described in Table 1 below.
TABLE 1SyntaxSizeNotesDL_Frame_Prefix_format( ) { Used subchannel bitmap6 bitsBit #0: subchannel group 0Bit #1: subchannel group 1Bit #2: subchannel group 2Bit #3: subchannel group 3Bit #4: subchannel group 4Bit #5: subchannel group 5 Reserved1 bitshall be set to zero Repetition_coding_indication2 bits0b00: No repetition coding on DL-MAP0b01: Repetition coding of 2 used on DL-MAP0b10: Repetition coding of 4 used on DL-MAP0b11: Repetition coding of 6 used on DL-MAP Coding_indication3 bits0b000: CC encoding used on DL-MAP0b001: BTC encoding used on DL-MAP0b010: CTC encoding used on DL-MAP0b011: ZT CC encoding used on DL-MAP0b100: CC encoding with optional interleaver0b101: LDPC encoding used on DL-MAP0b110-0b111: Reserved DL-MAP length8 bits— Reserved4 bitsshall be set to zero}
As shown in Table 1, the M-FCH includes sub-channel group information (i.e., Used subchannel bitmap), DL-MAP repetition coding indication information (i.e., Repetition_coding_indication), DL-MAP coding indication information (i.e., Coding_indication), and DL-MAP length information (i.e., DL-MAP length).
Similar to the BS-MS area, the BS transmits to the RS a MAP including allocation information on the BS-RS area and the RS obtains the allocation information by decoding the MAP. Therefore, in order for the RS to process the MAP there is a need to define signaling such as the M-FCH of Table 1.